The proposed studies are a continuation of investigation on the regional morphology of the myelinated axon and of the demyelinated axon. During the past year we have conducted a series of correlative morphological and physiological studies on axons within a central white matter tract (see Exp. Neurol. 53: 115-128, Exp. Neurol. 53: 129-150, Brain Res. 113: 179-187). Our results provide a large body of normative data on the conduction properties of axons in a normal white matter tract. We have also studied the cytochemistry of the axon surface, both in normal peripheral nerve, and in the specialized electrocyte axons in the gymnotid Sternarchus (J. Neurol. Sci. 31: 1-11). Our results indicate that there are distinct structural differences between the axon membrane at the node of Ranvier and the internode. We now intend to study the regeneration of the Sternarchus electrocyte axons following extirpation. In particular, we plan to address the question of the cellular mechanisms which determine specificity during myelination and remyelination, and further study the cytochemistry of these highly differentiated axons. We hope that these studies will be of value in terms of more fully understanding the reparative mechanisms which determine remyelination in the demyelinating diseases. BIBLIOGRAPHIC REFERENCES: Galaburda, A.M. Waxman, S.G., Kemper, T.L., and Jones, H.R. Progressive multifocal deficit with disseminated subpial demyelination. J. Neuropath. and Exp. Neurol. 35:481-494 (1976). Quick, D.C., and Waxman, S.G. Specific staining of the axon membrane at nodes of Ranvier with ferric ion and ferrocyanide. J. Neurol. Sci. 31: 1-11 (1977).